In the field of pipelines, it is known to use a pipeline inspection gauge (PIG). These devices are typically each defined by a pair of seals that are spaced apart from one another by an intermediate body. In use, a PIG is forced down a pipeline by the fluid flowing therein.
Passage of the PIG through a length of pipeline scours the walls somewhat. Accordingly, regular passage of PIGS through pipelines can avoid fouling and improve flow.
When a PIG placed in a pipeline fails to travel as expected, it is indicative of a need for further examination and possibly, of repair.
It is also known to fit a PIG with a gauge plate. When a PIG of this type is passed through a length of pipeline and exits with a deformed gauge plate, it can be indicative of a partial blockage, but false positives are known to occur.